1. Field of the Invention
The present invention relates to an optical apparatus such as a camera adapted for use of a film of the kind having a magnetic recording part, and more particularly to measures against magnetic noise applied to a magnetic head of the optical apparatus.
2. Description of Related Art
The photographic film of the kind having a magnetic recording layer formed on the base surface side thereof has become practically usable. A camera arranged to magnetically record information of varied kinds at each of photo-taking frames of the film of the above-stated kind was disclosed in U.S. Pat. No. 4,878,075, etc. For the photographic film of this kind, another camera has been developed to have a reloading function. According to the reloading function, in a case where the film has been reloaded on the same or some other camera after the use of the film is suspended by rewinding the film halfway before it is completely used, magnetic information recorded on the film is read by a magnetic head (magnetic reading means) disposed within the camera, so that a photo-taking operation on the same film from an unexposed (unused) frame part thereof can be resumed automatically.
In the meantime, the magnetic recording layer of the photographic film is formed to cover the whole film including photo-taking areas. However, the magnetic material of the magnetic layer is applied to the film in a very small quantity so as to prevent any adverse effect on picture quality. Therefore, the filling rate of the magnetic material is very small to give only a very small output of the magnetic head in reading the magnetic information recorded on the film.
It is, on the other hand, important for the magnetic reading device of a camera using the photographic film of the above-stated kind, to be compact in size. With the magnetic reading device compactly arranged within the camera, however, a magnetic noise generating source, such as a film transport motor, is disposed close to the magnetic head of the magnetic reading device. In many cases, the magnetic noise generating source thus imparts an induced noise component to the reading output of the magnetic head. As a result, the S/N ratio of the reading output is deteriorated to hinder the magnetic information from being accurately read by the magnetic reading device.
Cameras of the kind having the above-stated film reloading function are mostly arranged to make a check for the presence or absence of the record of magnetic information for every one of photo-taking frames and to determine each frame to be "exposed" when the frame is found to have the magnetic information. However, in a case where the induced noise component is large as compared with the reading output expected, detection of such a large induced noise component tends to cause an unexposed frame to be mistaken for an exposed frame. In such a case, the film reloading function cannot be adequately carried out.
To solve this problem, an arrangement has been proposed as disclosed in Japanese Laid-Open Patent Application No. HEI 4-22937, in which in order to lessen the adverse effect of an induced noise due to a film transport motor, a magnetic head is disposed in a specific direction with respect to the rotating shaft of the motor, because magnetism generated by the motor becomes less in that specific direction.
In connection with the above-stated problem, another arrangement has been proposed as disclosed in Japanese Laid-Open Patent Application No. HEI 5-34798, in which magnetism coming from a film transport motor is lessened by encompassing the motor with a magnetic shield member which is made of a suitable material. In the case of this disclosure, a soft magnetic material such as permalloy is employed as the magnetic shield member.
Another method has been proposed as disclosed in Japanese Laid-Open Patent Application No. HEI 4-32086, as a solution of the above-stated problem. According to this method, the adverse effect of magnetism coming from a motor is lessened by arranging a magnetic shield member either in front or in rear of a magnetic head.
A further method has been proposed as disclosed in connection with this problem in Japanese Laid-Open Patent Application No. HEI 6-332064. According to that method, an adverse effect of a leakage magnetic flux from a film transport motor on magnetic information recorded on the film is prevented by making, from a magnetic material, a film take-up spool with which to encompass the film transport motor.
However, these prior methods have presented the following problems. The induced noise generated at the magnetic head by the film transport motor cannot be sufficiently removed. In order to sufficiently attain the effect of these methods, the shield member must be arranged to have a large thickness and also to have a large area. However, such arrangement results in an increase in size of the magnetic reading device.